This invention relates generally to fluid sampling and more particularly to maintaining oxygen concentrations in a sample of water during benthic flux rate sampling.
Sediment in many bays, harbors and coastal waters is contaminated with metal and organic toxins. These toxins are known to cause extensive biological harm to aquatic environments. As a result of the threat of biological harm, remedies for contamination due to toxins are continually being devised.
In order to effectuate a satisfactory remedy however, the source of contamination must be identified. The remedial urgency (i.e. biological risk) relative to other contaminated sites must also be determined. With toxin sources identified and biological risk assessed, remedial resources can be efficiently allocated.
Historically, industrial discharge, chemical spills, improper waste disposal and urban runoff have been the largest known toxin sources. These sources are easily identifiable so that toxin discharge is controllable. Now, a significant portion of aquatic contamination is believed to come via pore water and particulate bound contaminate exchange in benthic sediment (i.e. soluble toxins are suspended and leached from underwater sediment into the aquatic environment).
Sedimentary (benthic) contamination is particularly troublesome to remedy because, unlike contamination caused by chemical spills and industrial discharge, the toxin source is often difficult to identify. Benthic contamination also creates a high level of biological risk for benthic organisms whose survival depends directly on the condition of the underwater sediment. Additionally, all aquatic organisms are put at risk of contamination as toxins in the underwater sediment migrate across the sediment-water interface and contaminate the aquatic environment. Due to the scope and seriousness of problems associated with benthic contamination, ways of assessing the biological risk associated with toxins in benthic sediments have been developed.
The biological risk is dependent, not only on toxin concentrations, but on the rate at which marine plants and animals uptake and accumulate harmful toxins. This rate must be determined. Direct measurement, however, of uptake and accumulation is extraordinarily difficult. Fortunately, indirect measurement is possible. This is accomplished by measuring the rate at which soluble toxins become suspended, leach through pore water, cross the sediment water boundary and enter the aquatic environment. This is called the benthic flux rate.
The benthic flux rate is the most accurate known indicator of the rate at which toxins are entering an aquatic environment and of associated biological risk. The benthic flux rate also is useful in pin pointing the source of contamination by determining whether toxins are leaching from the sediments into the water or vice versa. Together with traditional monitoring and assessment techniques, benthic flux measurements are useful in remedying contamination of benthic sediments.
At present, the best known approach for measuring the benthic flux rate requires isolating a volume of water against a water body floor and periodically sampling the isolated water. In this way, toxin concentration measurements are periodically made and changes in these concentrations are detected. Importantly, because changes in toxin concentrations are generally very small, other factors which could affect toxin concentration measurements and mislead researchers must be eliminated.
Many biological and geochemical processes are affected by dissolved oxygen contained in water samples. Oxygen conditions must, therefore, be maintained during sampling to obtain results which are accurately reflective of the natural environment. More specifically, respiration and oxidation processes tend to deplete oxygen. In the ocean, this depleted oxygen is normally replaced by oxygen introduced through the water-air interface through wave action and through various biological processes such as photosyntheses. In an isolated sample, however, depleted oxygen is not adequately replaced. As a result, oxygen dependent reactions which affect toxin levels fail to continue in a normal manner and make benthic toxicant flux rate measurements inaccurate.
In view of the inaccuracy caused by oxygen depletion while isolating fluid during sampling, a need has been recognized in accordance with this inventive concept for an improved method and apparatus for introducing oxygen into a closed benthic flux sampling chamber and maintaining appropriate oxygen levels to insure the integrity of the benthic flux sampling process and to allow precise and accurate benthic flux rate determinations.